fix #30048, lowering gc_preserve of closure variables (#30051)

src/julia-syntax.scm

@@ -3893,8 +3893,9 @@ f(x) = yt(x)
              '(null))
 
             ((gc_preserve_begin)
-             (let ((s (make-ssavalue)))
-               (emit `(= ,s ,e))
+             (let ((s    (make-ssavalue))
+                   (args (compile-args (cdr e) break-labels linearize-args)))
+               (emit `(= ,s ,(cons (car e) args)))
                s))
 
             ;; metadata expressions

test/syntax.jl

@@ -1736,6 +1736,21 @@ end
 # we don't parse chains of these since the associativity and meaning aren't clear
 @test_throws ParseError Meta.parse("1..2..3")
 
+# issue #30048
+@test Meta.isexpr(Meta.lower(@__MODULE__, :(for a in b
+           c = try
+               try
+                   d() do
+                       if  GC.@preserve c begin
+                           end
+                       end
+                   end
+               finally
+               end
+           finally
+           end
+       end)), :thunk)
+
 # issue #28506
 @test Meta.isexpr(Meta.parse("1,"), :incomplete)
 @test Meta.isexpr(Meta.parse("1, "), :incomplete)